Image processing system, projector, computer-readable medium, and image processing method

ABSTRACT

An image processing system and a projector project a calibration image onto a projection target, sense the calibration image to generate sensing information, and generate projection target region information based on the sensing information. The system and projector generate projection area information based on the sensing information, image distortion correction information based on the projection target region information and the projection area information, and correct an image signal based on the image distortion correction information so that image distortion is corrected. The system and projector project an image based on the image signal corrected by the distortion correction section, determine a first height/width ratio that indicates a height/width ratio of the projection target, generate the image distortion correction information to display an image at a first height/width ratio range and display an image at a desired height/width ratio when the first height/width ratio is not within the acceptable range.

This is a Continuation of application Ser. No. 10/880,642 filed Jul. 1, 2004, which claims priority of Japanese Patent Application No. 2003-270320, filed on Jul. 2, 2003, and Japanese Patent Application No. 2004-78412, filed on Mar. 18, 2004, which are hereby incorporated by reference in their entirety.

BACKGROUND

The present invention relates to an image processing system, a projector, a program, an information storage medium, and an image processing method capable of correcting image distortion.

An image may be distorted due to the relative angle formed by the optical axis of projection light from an image projection device such as a projector and a projection target such as a screen, whereby keystone distortion may occur in the vertical direction or horizontal direction.

Therefore, the image display device must display an image while eliminating distortion of the image.

A conventional projector with an image distortion correction function corrects image distortion only in the vertical direction using a built-in angle sensor, and cannot correct image distortion in the horizontal direction.

In the case of correcting image distortion in the horizontal direction, a user points at the four corners of the screen using a mouse or the like, and the projector semi-automatically corrects image distortion based on the point information. However, it is troublesome for the user to point at the four corners of the screen using a mouse or the like.

In order to solve such a problem, Japanese Patent Application Laid-open No. 2000-241874 has disclosed an automatic screen position adjustment device for a projector which detects the position of the screen in an image sensed by using a monitor camera based on an image signal input from the monitor camera, and adjusts keystone distortion of the projected image based on the detected screen position data.

In the method disclosed in Japanese Patent Application Laid-open No. 2000-241874, keystone distortion is adjusted by comparing the lengths of opposite sides of the screen in the sensed monitor screen as described in the specification of Japanese Patent Application Laid-open No. 2000-241874.

However, in the case where the height/width ratio (aspect ratio) of the projection target such as the screen is unknown, the projector cannot appropriately determine image distortion merely by comparing the lengths of opposite sides of the screen.

Japanese Patent application Laid-open No. 2002-247614 has disclosed a projector which detects the external shape of a screen by using a sensing section, and corrects an image so that the image has an external shape the same as the detected external shape.

However, if the projector changes the shape of the image into the external shape of the screen as disclosed in Japanese Patent application Laid-open No. 2002-247614, the image after changing has an external shape differing from the external shape of the original image. In this case, since an observer is given an impression differing from the original image, it is not preferable to employ such a processing method.

Moreover, it is preferable that a projected image be displayed at a desired height/width ratio even if the height/width ratio of the projection target is used as a reference.

SUMMARY

Exemplary embodiments of the broad principles described herein provide an image processing system, a projector, a program, and an image processing method that project a calibration image onto a projection target, sense the calibration image to generate sensing information, and generate projection target region information based on the sensing information. The system, projector, program, and method generate projection area information based on the sensing information, generate image distortion correction information based on the projection target region information and the projection area information, and correct an image signal based on the image distortion correction information so that image distortion is corrected. The system, projector, program, and method further project an image based on the image signal that has been corrected by the distortion correction section, determine a first height/width ratio that indicates a height/width ratio of the projection target based on the projection target region information, generate the image distortion correction information so that an image is displayed at the first height/width ratio when the first height/width ratio is within an acceptable range, and the image is displayed at a second height/width ratio that indicates a desired height/width ratio when the first height/width ratio is not within the acceptable range.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing a state during image projection;

FIG. 2 is a functional block diagram of a projector according to an example of an embodiment of the present invention;

FIG. 3 is a hardware block diagram of a projector according to an example of an embodiment of the present invention;

FIG. 4 is a flowchart showing a flow of image processing according to an example of an embodiment of the present invention;

FIG. 5 is a schematic diagram showing a sensing region according to an example of an embodiment of the present invention;

FIG. 6 is a schematic diagram showing the relationship between an angle .theta. and a distance L;

FIG. 7 is a schematic diagram of an XYZ three-dimensional space according to an example of an embodiment of the present invention;

FIG. 8 is a schematic diagram of a projection area after correction according to an example of an embodiment of the present invention;

FIG. 9 is a schematic diagram of a sensing plane of a sensor according to an example of an embodiment of the present invention.;

FIG. 10 is a schematic diagram showing coordinates of four corners of a projection area after correction according to an example of an embodiment of the present invention;

FIG. 11 is a two-dimensional look-up table showing coordinates of four corners of a projection area after correction according to an example of an embodiment of the present invention;

FIG. 12 is a schematic diagram showing a sensing region in an example of an embodiment of the present invention;

FIG. 13 is a schematic diagram in the case where a screen according to an example of an embodiment of the present invention is perspectively projected by using a sensor as the origin;

FIG. 14 is a schematic diagram in the case of changing a variable s in an example of an embodiment of the present invention;

FIG. 15A shows a screen in which the width is greater than the height, and FIG. 15B is view showing a projection area after correction on the screen shown in FIG. 15A;

FIG. 16A shows a screen in which the height is greater than the width, and FIG. 16B is view showing a projection area after correction on the screen shown in FIG. 16A;

FIG. 17 is a schematic diagram showing a projection area after correction in a sensing region in an example of an embodiment of the present invention;

FIG. 18 is a schematic diagram in the case where a projection area after correction according to an example of an embodiment of the present invention is perspectively projected with respect to a sensor as the origin;

FIG. 19 shows an arithmetic expression for determining coordinate transformation parameters according to an example of an embodiment of the present invention.

DETAILED DESCRIPTION OF EMBODIMENTS

The present invention is described below with reference to the drawings taking the case of applying the present invention to a projector which corrects image distortion as an example. Note that the embodiments described below do not in any way limit the scope of the invention defined by the claims laid out herein. Note also that all the elements of the embodiments described below should not be taken as essential requirements for the invention defined by the claims laid out herein.

First Embodiment

FIG. 1 is a schematic diagram showing a state during image projection.

A projector 20 which is one type of an image processing system projects an image onto a screen 10 which is one type of a projection target. In the present embodiment, the projector 20 is not perpendicular to the screen 10. A projected image 12 formed by projection light from the projector 20 is larger than the screen 10. In the present embodiment, a wall exists behind the screen 10 and reflects the projection light to allow the projected image 12 to be displayed.

In the present embodiment, a sensor 60 which is a part of a sensing means senses a region including the projected image 12.

In the present embodiment, the projector 20 calculates the aspect ratio (height/width ratio) of the screen 10 based on sensing information from the sensor 60. The projector 20 corrects image distortion based on the calculated aspect ratio and a known aspect ratio of the projected image so that the projected image 12 is displayed within the screen 10 and has an aspect ratio equal to that of the projected image.

Functional blocks of the projector 20 for implementing the above-described function is described below.

FIG. 2 is a functional block diagram of the projector 20 according to an example of the present embodiment.

The projector 20 includes a signal input section 110 to which an image signal is input, a distortion correction section 130 which corrects the input image signal so that image distortion is corrected, a signal output section 160 which outputs the corrected image signal, an image projection section 190 which is one type of an image projection means that projects an image based on the image signal, and a calibration image information generation section 170 which generates calibration image information.

The projector 20 includes a sensing section 180 which generates sensing information by sensing a region 8 including the projected image 12 through a sensing plane, a projection target region information generation section 140 which is one type of projection target region information generation means that detects the region of the screen 10 in the sensing region of the sensor 60 based on the sensing information, a projection area information generation section 150 which detects the region of the projected image 12 in the sensing region of the sensor 60, and a correction information generation section 120 which generates distortion correction information. The sensing section 180 includes the sensor 60.

The image projection section 190 includes a spatial light modulator 192, a driver section 194 which drives the spatial light modulator 192, a light source 196, and a lens 198.

The driver section 194 drives the spatial light modulator 192 based on the image signal from the signal output section 160. The image projection section 190 projects light from the light source 196 through the spatial light modulator 192 and the lens 198.

As hardware for implementing each section of the projector 20, the following hardware may be applied, for example.

FIG. 3 is a hardware block diagram of the projector 20 according to an example of the present embodiment.

For example, each section of the projector 20 may be implemented by using an A/D converter 930 or the like as the signal input section 110, an image processing circuit 970, RAM 950, CPU 910, or the like as the distortion correction section 130, a D/A converter 940 or the like as the signal output section 160, the image processing circuit 970, RAM 950, or the like as the correction information generation section 120, projection target region information generation section 140, projection area information generation section 150, and calibration image information generation section 170, a CCD sensor, CMOS sensor, RGB sensor, or the like as the sensing section 180, and a liquid crystal panel 920, ROM 960 which stores a liquid crystal light valve driver which drives the liquid crystal panel 920, or the like as the spatial light modulator 192.

These sections can exchange information through a system bus 980.

Some or the entirety of these sections may be implemented by hardware such as a circuit or may be implemented by software such as a driver.

The function of the projection target region information generation section 140 and the like may be implemented by a computer by reading a program from an information storage medium 900 which stores a program for allowing the computer to operate as the projection target region information generation section 140 and the like.

As the information storage medium 900, a CD-ROM, DVD-ROM, ROM, RAM, HDD, or the like may be applied. The program reading method may be either a contact method or a noncontact method.

The above-described function may be implemented by downloading a program or the like for implementing each function from a host device or the like through a transmission line instead of reading from the information storage medium 900.

Description of Image Processing Flow

An image processing flow using these sections is described below.

FIG. 4 is a flowchart showing a flow of image processing according to an example of the present embodiment.

The calibration image information generation section 170 generates image information for an all-black single-color calibration image (entire image is black), and the signal output section 160 outputs a digital signal of the image information to the image projection section 190.

The image projection section 190 projects an all-black calibration image onto the screen 10 based on the digital signal (step S1). This allows an all-black calibration image to be displayed on the screen 10.

The sensing section 180 senses the region including the projected image 12 through the sensing plane to generate first sensing information (step S2). The sensing information refers to information which indicates a luminance value or an image signal value which can generate the luminance value, such as an XYZ value, for each pixel of the sensor 60, for example. The XYZ value is an international standard defined by International Commission on Illumination (CIE) and is one type of an image signal value for a device independent color.

FIG. 5 is a schematic diagram showing a sensing region 17 according to an example of the present embodiment.

The sensing region 17 is a region corresponding to the sensing plane at which the sensor 60 senses an image, and is a region schematically showing the sensing information of the sensor 60 in the shape of a quadrilateral. In more detail, a region of the sensing plane of a CCD sensor or the like applies to the sensing region 17, for example.

In the present embodiment, the optical axis of the sensor 60 and the optical axis of the lens 198 face in the same direction, and the projector 20 is not perpendicular to the screen 10. Therefore, when viewed from the sensor 60, the projection area 13 which is the region of the projected image 12 is seen in the shape of a quadrilateral in the same manner as the sensing region 17, and the projection target region 11 which is the region of the screen 10 is distorted, as shown in FIG. 5.

In the present embodiment, the projection target region information generation section 140 searches for the luminance value radially outward from the intersecting point P0 of the diagonals of the projection area 13, that is, the center P0 of the projection area 13 (which may not necessarily be the center, but may be near the center). The projection target region information generation section 140 detects a line segment P0P1 on which approximately the same luminance value continues from the center P0 as a part of the projection target region 11. The projection target region information generation section 140 performs the same processing at a position at an angle of .theta. to detect a line segment P0P2 as a part of the projection target region 11. The distance of the line segment is denoted by L.

FIG. 6 is a schematic diagram showing the relationship between the angle 74 and the distance L.

The distance L changes as shown in FIG. 6 as the angle .theta. (.theta. is 0-2.pi.) changes, and forms four peaks at angles .theta.1, .theta.2, .theta.3, and .theta.4, for example.

The projection target region information generation section 140 calculates the sensor coordinates of four corners A, B, C, and D of the projection target region 11 from the sensor coordinates of the center P0 of the sensing region 17 (coordinates in the sensing region 17) and the distances L1, L2, L3, and L4 at the angles .theta.1, .theta.2, .theta.3, and .theta.4.

The projection target region information generation section 140 generates projection target region information which shows the sensor coordinates of the four corners (step S3), and sends the projection target region information to the correction information generation section 120.

The calibration image information generation section 170 generates calibration information for a multi-color calibration image which includes a white image (which may not necessarily be white, but may be a single color such as gray close to white) formed by reducing the original image by an arbitrary factor such as ¼ at the center and in which the region outside the white image consists of a black image (which may not necessarily be black, but may be a single color such as gray close to black). The image projection section 190 projects the multi-color calibration image (step S4).

The sensing section 180 senses the region 8 including the projected image 12 of the multi-color calibration image projected onto the screen 10 to generate second sensing information (step S5).

As shown in FIG. 5, a white region 15 corresponding to the white image is formed inside the projection target region 11 by the second sensing information.

The projection area information generation section 150 compares the luminance value of each pixel in the white region 15 with the luminance value of each pixel in the projection target region 11 to detect the white region 15 at a constant luminance ratio (step S6).

The projection area information generation section 150 calculates the sensor coordinates of the projection area 13 by increasing the sensor coordinates of the four corners of the white region 15 by n which is the inverse of the reduction factor.

The projection area information generation section 150 generates the projection area information which indicates the sensor coordinates of the projection area 13 (step S7), and sends the projection area information to the correction information generation section 120.

The correction information generation section 120 derives the relative distance between the screen 10 and the sensor 60 on the optical axis of the sensor 60 (step S8).

In more detail, in the case where the sensor coordinates of the projection target region 11 are denoted by A(Ax, Ay), B(Bx, By), C(Cx, Cy), and D(Dx, Dy), in the XYZ three-dimensional space in which the optical axis of the sensor 60 is added to the two-dimensional plane XY of the sensing region 17 of the sensor 60 as a third dimension Z, the coordinates of the four corners of the screen 10 are denoted by A′(s*Ax, s*Ay, s*Pz), B′(t*Bx, t*By, t*Pz), C′(u*Cx, u*Cy, u*Pz), and D′(v*Dx, v*Dy, v*Pz). Pz is the distance on the Z axis from the origin of the sensor coordinate system to the virtual sensing plane as the sensing region 17. The projection target region information generation section 140 determines Pz by calculating Pz=(VR/2)/tan(.theta.c/2) based on the relationship between the horizontal view angle .theta.c and the horizontal resolution VR of the sensor 60.

FIG. 7 is a schematic diagram of the XYZ three-dimensional space according to an example of the present embodiment.

Since the screen 10 is known to be rectangular (may be square), the line segment A′B′ equals the line segment D′C′. t, u, and v are expressed as follows on the assumption that this condition is satisfied. t=s* {(Dy−Cy)*(Ax−Dx)−(Dx−Cx)*(Ay−Dy)}/{(Dy−Cy)*(Bx−Dx)−(Dx−Cx)*(By−Dy)} u=s* {(By−Dy)*(Ax−Dx)−(Bx−Dx)*(Ay−Dy)}/{(By−Dy)*(Dx−Cx)−(Bx−Dx)*(Dy−Cy)} v=s−t+u

The relative distances on the optical axis (Z-axis component) from the origin to the four corners A, B, C, and D of the screen 10 can be obtained by assuming that s is 1 (may not necessarily be 1).

The correction information generation section 120 calculates the aspect ratio of the screen 10 by comparing .vertline.A′B′.vertline. and .vertline.B′C′.vertline. which show the lengths of two sides of the screen 10 which are not opposite each other.

The correction information generation section 120 derives the projection area after correction (step S10).

FIG. 8 is a schematic diagram of a projection area 19 after correction according to an example of the present embodiment.

In the case where the aspect ratio of the projected image 12 is 4:3 and the aspect ratio of the screen 10 is 4:2, a region which is reduced by ⅙ from the right and left ends of the projection target region 11 in the sensing region 17 is the projection area 19 after correction. The aspect ratio of the projected image 12 is generally known such as 4:3 or 16:9.

The correction information generation section 120 transforms the coordinates of the projection area 19 after correction in the sensing region 17 into the image processing coordinates of the spatial light modulator 192 (step S11).

The correction information generation section 120 calculates the difference between the image processing coordinates of the spatial light modulator 192 after distortion correction and the image processing coordinates of the spatial light modulator 192 before distortion correction, and generates the difference as image distortion correction information.

The distortion correction section 130 corrects the image signal based on the image distortion correction information so that image distortion is corrected.

This enables the image projection section 190 to project an image after distortion correction.

As described above, according to the present embodiment, the external shape of the projection target (screen 10, for example) can be determined based on the difference in the image signal value (luminance value, for example) based on the sensing information.

According to the present embodiment, even if the calibration image 12 is projected at a size larger than the screen 10, the projector 20 can form a single-color region (white or gray close to white, for example) which is reduced in size while maintaining the shape of the original image on the screen 10 by using the multi-color calibration image.

The projector 20 can determine image distortion by sensing the single-color region formed on the projection target.

The image processing system or the like can determine the projection position of the image after distortion correction based on the height/width ratio of the projection target determined by sensing and the height/width ratio of the calibration image. The image processing system or the like can generate the image distortion correction information which indicates the degree of image adjustment required based on the difference between the projection position of the image after distortion correction and the projection position of the image before distortion correction, whereby distortion of the image can be appropriately corrected.

According to the present embodiment, the projector 20 can project an image at an original height/width ratio by generating the image distortion correction information so that the image is projected at the original height/width ratio instead of changing the shape of the image corresponding to the shape of the screen 10.

Therefore, according to the present embodiment, the projector 20 can automatically correct distortion of the projected image in the vertical direction and the horizontal direction which occurs during use of the projector 20 at an accurate aspect ratio. In particular, the projector 20 can correct image distortion without being restricted by the vertical and horizontal distortion detection angles of the image by correcting distortion utilizing the frame of the screen 10.

Since the linear component of the projection area after correction is in parallel to the frame of the screen 10, the projector 20 can display a visually recognizable image on the screen 10, even if the projector 20 is not installed perpendicular to the plane.

Since the projector 20 is rarely affected by an obstacle on the screen 10 by comparing the luminance value outward from the center when detecting the projection target region 11, the projector 20 can detect the projection target region 11 more accurately.

Modification of First Embodiment

The application of the present invention is not limited to the above-described embodiment.

In the above-described embodiment, the projector 20 uses the two-dimensional coordinates of the sensing region 17 of the sensor 60 and performs the processing on the assumption that the variable s is 1. However, the projector 20 may use the three-dimensional coordinates of the sensor 60 and set the variable s to a value conforming to the actual sensor 60.

FIG. 9 is a schematic diagram of the sensing plane of the sensor 60 according to an example of the present embodiment.

In the case where the horizontal resolution of the sensor 60 is denoted by W and the horizontal view angle of the sensor 60 is denoted by .theta.h, the variable Pz is expressed as (W/2)/tan(.theta.h/2).

The correction information generation section 120 transforms the three-dimensional coordinates A′, B′, C′, and D′ of the screen 10 from the sensor three-dimensional coordinate system (xc, yc, zc) into the projector three-dimensional coordinate system (xp, yp, zp). In more detail, the correction information generation section 120 may transform (xc, yc, zc, 1) into (xp, yp, zp, 1) by using a matrix with four rows and four columns, for example. The parameter in the matrix is determined by the positional relationship and the angular relationship between the sensor 60 and the projector 20.

The correction information generation section 120 calculates the normal vector N(Nx, Ny, Nz) of the screen 10 by using three points among the coordinates a(ax, ay, az) to d(dx, dy, dz) of the four corners of the screen 10 in the projector three-dimensional coordinate system.

In the case of calculating the normal vector by using a, c, and d, Nx=(dy−cy)*(az−dz)−(dz−cz)*(ay−dy), Ny=dz−cz)*(ax−dx)−(dx−cx)*(az−dz), and Zn=(dx−cx)*(ay−dy)−(dy−cy)*(ax−dx).

Since the angle formed by the normal vector N and the vector (0, 0, 1) (horizontal .theta.x, vertical .theta.y) corresponds to the angle formed by the screen 10 and the optical axis of the projection light of the projector 20, the correction information generation section 120 searches for the coordinates of the four corners of the projection area after correction from a two-dimensional look-up table by using .theta.x and .theta.y.

FIG. 10 is a schematic diagram showing the coordinates of the four corners of the projection area after correction according to an example of the present embodiment. FIG. 11 is a two-dimensional look-up table showing the coordinates of the four corners of the projection area after correction according to an example of the present embodiment.

As shown in FIG. 11, in the two-dimensional look-up table, the values for .theta.x and .theta.y are associated with the xy coordinates of the coordinates E, F, G, and H of the four corners of the projection area after correction.

The correction information generation section 120 generates the image distortion correction information using the xy coordinates of the coordinates E, F, G, and H utilizing the two-dimensional look-up table shown in FIG. 11, and sends the image distortion correction information to the distortion correction section 130.

This method also enables the projector 20 to correct image distortion based on the coordinates of the four corners of the screen 10.

Second Embodiment

The projector 20 for projecting an image at a given aspect ratio is described below.

For example, even if a part of the projected image 12 is projected outside the screen 10 as shown in FIG. 1, the projector 20 can sense the center region of the projected image inside the screen 10 by dividing the projected image 12 equally into nine regions and using the center region as a reference.

For example, the projector 20 can determine the position of the center region in the sensing region 17 of the sensor 60 by comparing each pixel of an all-black first calibration image with each pixel of a second calibration image in which the center region is white and eight peripheral regions are black.

FIG. 12 is a schematic diagram showing the sensing region 17 in an example of the present embodiment. FIG. 13 is a schematic diagram in the case where the screen 10 according to an example of the present embodiment is perspectively projected with respect to the sensor 60 as the origin.

In this case, the sensor 60 can sense the center region 15 inside the projection target region 11 in the sensing region 17.

A sensor coordinate system having the center of the sensing region 17 of the sensor 60 as the origin is considered below as an example. In the sensor coordinate system, the horizontal direction of the sensing region 17 is the x-axis, the vertical direction of the sensing region 17 is the y-axis, and the normal direction of the sensing region 17 is the z-axis.

The projection target region information generation section 140 generates the projection target region information which indicates the coordinates of the projection target region 11 in the sensor coordinate system. The projection area information generation section 150 generates the projection area information which indicates the coordinates of the projection area in the sensor coordinate system.

The coordinates of the four corners of the projection target region 11 in the sensing region 17 are denoted by E (Ex, Ey), F (Fx, Fy), G (Gx, Gy), and H (Hx, Hy). These two-dimensional coordinates correspond to the coordinates obtained by perspectively projecting four vertices E′, F′, G′, and H′ of the screen 10 which exists in the three-dimensional space onto a virtual sensing plane z=Pz which exists in the normal direction of the origin O of the sensor 60. The origin O is the center point of the sensing region 17.

Therefore, the sensor three-dimensional coordinates of the four vertices of the screen 10 perspectively projected onto the virtual sensing plane are expressed as E(Ex, Ey, Pz), F(Fx, Fy, Pz), G(Gx, Gy, Pz), and H(Hx, Hy, Pz) which have the same z-axis component. The projection target region information generation section 140 can determine Pz by calculating Pz=(VR/2)/tan(.theta.c/2) based on the relationship between the horizontal view angle .theta.c and the horizontal resolution VR of the sensor 60.

Since the four vertices of the actual screen 10 exist ahead of the vertices E, F, G, and H from the origin of the sensor 60, the four vertices of the screen 10 are expressed as s*E(Ex, Ey, Pz), t*F(Fx, Fy, Pz), u*G(Gx, Gy, Pz), and v*H(Hx, Hy, Pz). Note that s, t, u, and v are real numbers.

Since the screen 10 is rectangular, the side E′F′ and the side G′H′ are in parallel and equal in length and the side E′H′ and the side F′G′ are in parallel and equal in length. The projection target region information generation section 140 can determine the coordinates of the four vertices of the screen 10 in the three-dimensional coordinate system of the sensor 60 by solving s, t, u, and v based on the above condition, and the correction information generation section 120 can determine the aspect ratio of the screen 10 based on the determined coordinates.

From the above presupposition, E′F′=(t*Fx−s*Ex, t*Fy−s*Ey, t*Pz−s*Pz) and H′G′=(u*Gx−v*Hx, u*Gy−v*Hy, u*Pz−v*Pz).

And t*Fx−s*Ex equals u*Gx−v*Hx, t*Fy−s*Ey equals u*Gy−v*Hy, and t*Pz−s*Pz equals u*Pz−v*Pz. Therefore, t*Fx−u*Gx+v*Hx=s*Ex . . . (1), t*Fy−u*Gy+v*Hy=s*Ey. (2), and t*Pz+u*Pz+v*Pz=s*Pz . . . (3) are obtained.

Dividing the equation (3) by Pz yields t−u+v=s . . . (4).

Substituting the value obtained by multiplying the equation (4) by Hx into the equation (1) yields (Fx−Hx)*t+(Hx−Gx)*u=(Ex−Hx)*s . . . (5).

Substituting the value obtained by multiplying the equation (4) by Hx into the equation (2) yields (Fy−Hy)*t+(Hy−Gy)*u=(Ey−Hy)*s . . . (6).

In the equations (5) and (6), suppose that a=(Fx−Hx), b=(Hx−Gx), c=(Ex−Hx), d=(Fy−Hy), e=(Hy−Gy), and f=(Ey−Hy). In this case, the equation (5) is expressed as a*t+b*u=c*s, and the equation (6) is expressed as d*t+e*u=f*s.

Solving these equations yields t=s*(e*c−b*f)/(e*a−b*d) and u=s*(d*c−a*f)/(d*b−a*e). Specifically, t and u can be expressed by using s. The position of the screen 10 in the case of changing the variable s which shows the depth information is described below.

FIG. 14 is a schematic diagram in the case of changing the variable s in an example of the present embodiment.

As shown in FIG. 14, since the shape of the screen 10 is similar even if the variable s is changed, the aspect ratio is invariable. Therefore, the aspect ratio can be calculated by assuming that s=1. If s=1, t=(e*c−b*f)/(e*a−b*d), u=(d*c−a*f)/(d*b−a*e), and v−1−t*u.

The correction information generation section 120 calculates the aspect ratio by using the three-dimensional coordinates of the four vertices of the screen 10 based on the projection target region information from the projection target region information generation section 140. The aspect ratio used herein refers to the ratio of the length of the horizontal side of the target region to the length of the vertical side of the target region. In the case where horizontal length: vertical length=4:3, the aspect ratio is ¾=0.75. In the present embodiment, the projected image 12 is corrected so that the aspect ratio of the projected image 12 is 0.75.

FIG. 15A shows the screen 10 in which the width is greater than the height. FIG. 15B shows the projection area after correction on the screen 10 shown in FIG. 15A. FIG. 16A shows the screen 10 in which the width is smaller than the height. FIG. 16B shows the projection area after correction on the screen 10 shown in FIG. 16A.

In the case where the aspect ratio of the screen 10 is approximately equal to 0.75 (aspect ratio may not necessarily be equal to 0.75 insofar as it is in the allowable range), the correction information generation section 120 generates the correction information so that the shape of the projected image 12 corresponds to the shape of the screen 10. In the present embodiment, the correction information generation section 120 generates the correction information so that the shape of the projected image 12 corresponds to the shape of the screen 10 when the aspect ratio is 0.75 for convenience of description.

As shown in FIG. 15A, in the case where the aspect ratio is smaller than 0.75, specifically, the width of the screen 10 is greater than its height, the correction information generation section 120 generates the correction information so that the projection area A′B′C′D′ after correction is formed in the region smaller than the screen 10 on the right and left as shown in FIG. 15B.

In the case where the aspect ratio Sa is smaller than 0.75, since A′ is the point which divides E′H′ at a ratio of m:n, A′=(n*E′+m*H′)/(m+n). Note that m+n=1.

Since height:width of the screen 10=sa:1, it is necessary that m=(1−4*Sa/3)/2 and n=1−(1−4*Sa/3)/2 in order to maintain the aspect ratio of the projection area after correction at 0.75. The projection area information generation section 150 calculates B′, C′, and D′ in the same manner as A′.

As shown in FIG. 16A, in the case where the aspect ratio is greater than 0.75, specifically, the height of the screen 10 is greater than the width, the correction information generation section 120 generates the correction information so that the projection area A′B′C′D′ after correction is formed in the region smaller than the screen 10 at the top and bottom as shown in FIG. 16B.

In the case where the aspect ratio Sa is greater than 0.75, since A′ is the point which divides E′F′ at a ratio of m:n, A′=(n*E′+m*F′)/(m+n). Note that m+n=1.

Since height:width of the screen 10=sa:1, it is necessary that m=(Sa−¾)/2 and n=Sa−(Sa−¾)/2 in order to maintain the aspect ratio of the projection area after correction at 0.75. The projection area information generation section 150 calculates B′, C′, and D′ in the same manner as A′.

The projection area information generation section 150 generates the projection area information which indicates the coordinates A′, B′, C′, and D′ of the projection area after correction in this manner.

The correction information generation section 120 may generate the correction information so that the projection area after correction is increased to some extent based on the projection area information from the projection area information generation section 150. This enables image appearance to be improved as a frameless image. If the magnification factor is denoted by Ps and the intersecting point of the diagonal lines of the projection area after correction is denoted by P, the correction information generation section 120 calculates the vertex A′ of the projection area after magnification as shown by A′=Ps*PA′+OP. The correction information generation section 120 calculates B′, C′, and D′ in the same manner as A′.

A′, B′, C′, and D′ in the sensor coordinate system determined as described above are perspectively projected onto the screen 10. This transformation processing is performed by setting the depth information z at Pz.

For example, the correction information generation section 120 calculates the coordinates of the vertex A′ as A′x=A′x/A′z*Pz, A′y=A′y/A′z*Pz, and A′z=A′z/A′z*Pz. The correction information generation section 120 calculates B′, C′, and D′ in the same manner as A′.

FIG. 17 is a schematic diagram showing the projection area 19 after correction in the sensing region 17 in an example of the present embodiment. FIG. 18 is a schematic diagram in the case where the projection area after correction according to an example of the present embodiment is perspectively projected with respect to the sensor 60 as the origin.

The correction information generation section 120 transforms the coordinates of the projection area after correction on the screen 10 into the coordinates in a liquid crystal panel 920.

The correction information generation section 120 generates a coordinate transformation parameter based on the correspondence relationship between the known coordinates A(Ax, Ay), B(Bx, By), C(Cx, Cy), and D(Dx, Dy) of the four vortices of the center region in the sensor coordinate system and the coordinates I(Ix, Iy), J(Jx, Jy), K(Kx, Ky), and L(Lx, Ly) of the four vortices of the center region in the liquid crystal panel 920.

FIG. 19 shows an arithmetic expression for determining the coordinate transformation parameter according to an example of the present embodiment.

The correction information generation section 120 transforms the coordinates of the projection area A′B′C′D′ after correction into the coordinates in the liquid crystal panel 920 by using coordinate transformation parameters Pa to Ph shown in FIG. 19.

In the case of the vertex A′, A′x=(Pa*A′x+Pb*A′y+Pc)/(Pg*A′x+Ph*A′y−+1) and A′y=(Pd*A′x+Pe*A′y+Pf)/(Pg*A′x+Ph*A′y+1). This also applies to the vertices B′, C′, and D′.

The correction information generation section 120 generates the correction information based on the difference between the original coordinates in the liquid crystal panel 920 and the coordinates in the liquid crystal panel 920 after correction. The distortion correction section 130 corrects the image signal based on the generated correction information. The image projection section 190 projects an image based on the corrected image signal.

This enables the projector 20 to project an image without distortion at the center of the screen 10 by effectively utilizing the screen 10 as much as possible.

As described above, according to the present embodiment, the projector 20 can project an image at a desired aspect ratio by effectively utilizing the region of the screen 10. This enables the projector 20 to project an image which is easily seen by an observer without being affected by the shape of the screen 10.

Moreover, the projector 20 can appropriately correct an image without being affected by the difference in position between the projector 20 and the sensor 60 by calculating the coordinates using the sensor coordinate system. Therefore, various types of sensing means such as a sensor included in the projector 20, a sensor positioned at a distance from the projector 20, or a digital camera can be employed as the sensor 60.

Modification

The present invention is not limited to the above-described embodiments. Various modifications and variations can be made.

The present invention is particularly effective in the case where the projected image 12 includes the screen 10. For example, the projector 20 may automatically detect the inclusion relationship between the projected image 12 and the screen 10, and determine the image correction method to be applied corresponding to the detection result.

In the case where the projector 20 has a zoom function, the projector 20 may project an image by performing zoom adjustment so that the projected image 12 includes the screen 10, for example.

In the above-described embodiments, the projected image 12 is divided equally into nine regions and the center region is used as the reference. However, the size and position of the center region may be arbitrary insofar as the projector 20 can include the center region of the projected image inside the screen 10.

In the above-described embodiments, the screen 10 is used as the projection target. However, the projection target may be a white board, wall, or the like insofar as the projection target is in the shape of a quadrilateral which allows detection of the four corners.

In the above-described embodiments, the projector 20 is used as the image processing system. However, the present invention is also effective for an image processing system for a display such as a cathode ray tube (CRT), light emitting diode (LED), or electroluminescence (EL) in addition to the projector 20.

As the projector 20, a liquid crystal projector, a projector using a digital micromirror device (DMD), or the like may be used. DMD is a trademark of Texas Instruments, Inc. (U.S.A.).

The function of the projector 20 may be implemented by only a projector, or may be distributed in a plurality of processing devices (distributed processing of projector and PC, for example). 

1. An image processing system comprising: an image projection means for projecting a calibration image onto a projection target; a sensing means for sensing the calibration image to generate sensing information; a projection target region information generation means for generating projection target region information based on the sensing information; a projection area information generation means for generating projection area information based on the sensing information; a correction information generation means for generating image distortion correction information based on the projection target region information and the projection area information; and a distortion correction means for correcting an image signal based on the image distortion correction information so that image distortion is corrected; the image projection means projecting an image based on the image signal that has been corrected by the distortion correction means, and the correction information generation means determining a first height/width ratio that indicates a height/width ratio of the projection target based on the projection target region information, and generating the image distortion correction information so that an image is displayed at the first height/width ratio when the first height/width ratio is within an acceptable range, and the image is displayed at a second height/width ratio that indicates a desired height/width ratio when the first height/width ratio is not within the acceptable range.
 2. The image processing system as defined in claim 1, the correction information generation means: calculating a relative distance between an origin in a three-dimensional space in which an optical axis of the sensing means is added to a two-dimensional plane of the sensing region as a third dimension and four corners of the projection target on the optical axis based on the projection target region information; calculating coordinates of the four corners of the projection target in the three-dimensional space based on the projection target region information and the relative distance; and calculating a first height/width ratio by calculating lengths of two sides of the projection target that are not opposite each other based on the coordinates.
 3. The image processing system as defined in claim 1, wherein the projection target region information generation means searching for an image signal value of the sensing information so that each pixel is radially searched for from a region near a center of the sensing region, and generating the projection target region information by determining the projection target region based on a difference in the image signal value during searching.
 4. An image processing system comprising: an image projection section that projects a calibration image onto a projection target; a sensing section that senses the calibration image to generate sensing information; a projection target region information generation section that generates projection target region information based on the sensing information; a projection area information generation section that generates projection area information based on the sensing information; a correction information generation section that generates image distortion correction information based on the projection target region information and the projection area information; and a distortion correction section that corrects an image signal based on the image distortion correction information so that image distortion is corrected; the image projection section projecting an image based on the image signal that has been corrected by the distortion correction section, and the correction information generation section determining a first height/width ratio that indicates a height/width ratio of the projection target based on the projection target region information, and generating the image distortion correction information so that an image is displayed at the first height/width ratio when the first height/width ratio is within an acceptable range, and the image is displayed at a second height/width ratio that indicates a desired height/width ratio when the first height/width ratio is not within the acceptable range.
 5. A projector comprising: an image projection means for projecting a calibration image onto a projection target; a sensing means for sensing the calibration image to generate sensing information; a projection target region information generation means for generating projection target region information based on the sensing information; a projection area information generation means for generating projection area information based on the sensing information; a correction information generation means for generating image distortion correction information so that an image is projected onto the projection target region at a desired height/width ratio, based on the projection target region information and the projection area information; and a distortion correction means for correcting an image signal based on the image distortion correction information so that image distortion is corrected; the image projection means projecting an image based on the image signal that has been corrected by the distortion correction means, and the correction information generation means determining a first height/width ratio that indicates a height/width ratio of the projection target based on the projection target region information, and generating the image distortion correction information so that an image is displayed at the first height/width ratio when the first height/width ratio is within an acceptable range, and the image is displayed at a second height/width ratio that indicates a desired height/width ratio when the first height/width ratio is without the acceptable range.
 6. A projector comprising: an image projection section that projects a calibration image onto a projection target; a sensing section that senses the calibration image to generate sensing information; a projection target region information generation section that generates projection target region information based on the sensing information; a projection area information generation section that generates projection area information based on the sensing information; a correction information generation section that generates image distortion correction information so that an image is projected onto the projection target region at a desired height/width ratio based on the projection target region information and the projection area information; and a distortion correction section that corrects an image signal based on the image distortion correction information so that image distortion is corrected; the image projection section projecting an image based on the image signal that has been corrected by the distortion correction section, and the correction information generation section determining a first height/width ratio that indicates a height/width ratio of the projection target based on the projection target region information, and generating the image distortion correction information so that an image is displayed at the first height/width ratio when the first height/width ratio is within an acceptable range, and the image is displayed at a second height/width ratio that indicates a desired height/width ratio when the first height/width ratio is not within the acceptable range.
 7. A computer-readable medium comprising a computer-readable program executed by a computer, the computer including an image projection section, a sensing section, a projection target region information generation section, a projection area information generation section, a correction information generation section, a distortion correction section, and an image projection section, the program causing the computer to perform processing for: the image projection section to project a calibration image onto a projection target; the sensing section to sense the calibration image to generate sensing information; the projection target region information generation section to generate projection target region information based on the sensing information; the projection area information generation section to generate projection area information based on the sensing information; the correction information generation section to generate image distortion correction information so that an image is projected onto the projection target region at a desired height/width ratio, based on the projection target region information and the projection area information; and the distortion correction section to correct an image signal based on the image distortion correction information so that image distortion is corrected; the image projection section projecting an image based on the image signal that has been corrected by the distortion correction section, and the correction information generation section determining a first height/width ratio that indicates a height/width ratio of the projection target based on the projection target region information, and generating the image distortion correction information so that an image is displayed at the first height/width ratio when the first height/width ratio is within an acceptable range, and the image is displayed at a second height/width ratio that indicates a desired height/width ratio when the first height/width ratio is not within the acceptable range.
 8. An image processing method comprising: projecting a calibration image onto a projection target; sensing the calibration image to generate sensing information; generating projection target region information based on the sensing information; generating projection area information based on the sensing information; determining a first height/width ratio that indicates a height/width ratio of the projection target based on the projection area information; determining whether the first height/width ratio is within an acceptable range; generating image distortion correction information so that an image is displayed at the first height/width ratio when the first height/width ratio is within the acceptable range, and the image is displayed at a second height/width ratio that indicates a desired height/width ratio when the first height/width ratio is not within the acceptable range; correcting an image signal based on the image distortion correction information so that image distortion is corrected; and projecting an image based on the corrected image signal.
 9. The image processing method as defined in claim 8, the method further comprising: calculating a relative distance between an origin in a three-dimensional space in which an optical axis of the sensing section is added to a two-dimensional plane of the sensing region as a third dimension and four corners of the projection target on the optical axis based on the projection target region information; calculating coordinates of the four corners of the projection target in the three-dimensional space based on the projection target region information and the relative distance; and calculating a first height/width ratio by calculating lengths of two sides of the projection target that are not opposite each other based on the coordinates.
 10. The image processing method as defined in claim 8, the method further comprising: searching for an image signal value of the sensing information so that each pixel is radially searched for from a region near a center of the sensing region, and generating the projection target region information by determining the projection target region based on a difference in the image signal value during searching when generating the projection target region information. 